The invention relates to a dryer-ironer wherein laundry is ironed between a heated ironing cylinder and one or more endless straps which are in contact with the cylinder on a portion of its circumference.
The dryer-ironer according to the invention may be used in all cases where relatively large amounts of laundry must be ironed frequently. Thus and uniquely as an example, such a machine may be used in hospital institutions, nursing homes, hotels, lodging houses, restaurants, etc.
In dryers-ironers with a heated ironing cylinder, the pieces of laundry are inserted one after the other between a rotating cylinder, with a generally horizontal axis, and one or more endless straps which are in contact with the cylinder along its entire length and a portion of its circumference. Heating means placed inside the cylinder bring the latter""s metal wall up to a determined temperature, selected in order to provide effective ironing of the laundry.
The heating means which are placed inside the ironing cylinder are of different types, depending on the machines. Hence, these heating means may comprise a gas manifold, heating resistances, infrared heating devices, etc.
In existing dryers-ironers, the ironing cylinder has a relatively thick cylindrical wall. This wall is generally made of steel. It has relatively large thermal inertia, because of its thickness.
In a dryer-ironer of this type, the passing of a piece of laundry with a given width between the ironing cylinder and the endless straps has the effect of lowering the temperature of the cylinder in the concerned area. On the contrary, the areas of the cylinder not concerned by the passing of the piece of laundry and which continue to be heated, experience a rise in their temperature. Considering the relatively large thermal inertia of the ironing cylinder, a piece of laundry immediately ironed after the previous one will therefore encounter either an insufficiently heated area of the cylinder or on the contrary an overheated area of the cylinder, depending on whether it is inserted at the same place than the previous piece of laundry or at a different place. In the first case, the second piece of laundry is badly ironed. On the contrary, in the second case, the piece of laundry may be burnt. Actually, the thermal gradient even increases if several pieces of laundry are successively inserted substantially in the same area.
Dryers-ironers with a heated ironing cylinder are also known, wherein heating of the cylinder is provided by a heat carrying fluid such as oil. In this case, the heat carrying fluid is heated in a boiler located outside the machine, before being fed into the cylinder by a pump also placed outside the machine.
Such a machine does not have the drawbacks of dryers-ironers for which the ironing cylinder is heated by heating means integrated into this cylinder. Actually, permanent circulation of the heat carrying fluid is able to provide efficient diffusion of the heat over the entire length of the cylinder and consequently, to impart to the latter, a substantially uniform temperature over its entire length even after the passing of a piece of laundry in the machine.
On the other hand, the dryers-ironers of this type have the drawbacks of requiring heavy, external, expensive and complex facilities.
This drawback sometimes causes the users to simultaneously feed several machines by a unique circuit integrating one single boiler and one single pump. However, the cost of such a facility remains substantially greater than that of a dryer-ironer for which the ironing cylinder is heated by an integrated heating system.
Specifically, the object of the invention is a dryer-ironer with a heated ironing cylinder, having both the advantages of simplicity of machines with integrated heating in the cylinder and the advantages of uniform diffusion of heat over the entire length of the cylinder of machines for which the cylinder is heated by a heat carrying fluid.
According to the invention, this result is obtained by means of a dryer-ironer comprising an ironing cylinder provided with a cylindrical wall and able to rotate about an axis of said wall, and heating means placed inside the cylinder, in order to heat the cylindrical wall, characterized in that the cylinder further comprises an external wall, encircling the cylindrical wall in order to delimit with the latter an closed annular chamber, filled with a heat carrying fluid, and stirring means able to generate a circulation of the heat carrying fluid within said chamber, wherein said stirring means comprise units placed in the annular chamber.
In this machine, the ironing cylinder is heated from the inside by traditional heating means, which may be of any type, as in the existing machines for which the cylinder is heated from the inside. Moreover, by using an ironing cylinder with a double wall, by filling the closed annular chamber thus defined by a heat carrying fluid and by using means for stirring this fluid, integrated into the cylinder, an efficient diffusion of heat on the entire length of the cylinder may be provided without substantially increasing the complexity and the cost of the machine.
According to a first embodiment of the invention, the aforementioned units are passive units, placed in the annular chamber in order to generate circulation of the heat carrying fluid when the cylinder is rotating around its axis.
These passive units comprise, for example, blades supported by the cylindrical wall, wherein these blades are inclined with respect to the cylinder""s axis, so as to generate motion of the heat carrying fluid, parallel to the axis of the cylinder, upon the latter""s rotation.
Preferably, the blades have a height substantially equal to the thickness of the annular chamber, in order to also serve as support for the external wall of the cylinder.
In the first embodiment of the invention, the heat carrying fluid is a liquid which only fills a portion of the annular chamber. This liquid is topped by a neutral gas, so that the annular chamber also acts as an expansion vessel.
Advantageously, stabilizers such as balls are then placed in the liquid in order to oppose a rotation of the latter with the cylinder when the latter rotates around its axis.
According to a second embodiment of the invention, the aforementioned units are partitions in a staggered configuration within the annular chamber, in order to delimit between the cylindrical wall and the external wall of the cylinder, a path for reciprocating motion, substantially parallel to the axis of the cylinder. Now, the stirring means further comprise driving means such as a pump in order to cause circulation of the heat carrying fluid along this path.
In both embodiments of the invention, the external wall preferably has a thickness lower than that of the cylindrical wall.
Moreover, the external wall of the cylinder is advantageously made of stainless steel and the cylindrical wall of ordinary steel.
Preferably, at least one end of the external wall is encircled by a discharge space, externally delimited by a fixed case. A valve is then mounted in the aforementioned end of the external wall so as to allow the annular chamber to communicate with the discharge space, in the event of overpressure in said chamber.
Advantageously, a duct connects the discharge space to a tank, in order to provide flow by gravity of the heat carrying fluid.